title: Negative regulation of Toll-like receptor 4 signaling by IL-10-dependent microRNA-146b.
abstract: Toll-like receptors (TLRs) play key roles in detecting pathogens and initiating inflammatory responses that, subsequently, prime specific adaptive responses. Several mechanisms control TLR activity to avoid excessive inflammation and consequent immunopathology, including the anti-inflammatory cytokine IL-10. Recently, several TLR-responsive microRNAs (miRs) have also been proposed as potential regulators of this signaling pathway, but their functional role during the inflammatory response still is incompletely understood. In this study, we report that, after LPS engagement, monocytes up-regulate miR-146b via an IL-10-mediated STAT3-dependent loop. We show evidence that miR-146b modulates the TLR4 signaling pathway by direct targeting of multiple elements, including the LPS receptor TLR4 and the key adaptor/signaling proteins myeloid differentiation primary response (MyD88), interleukin-1 receptor-associated kinase 1 (IRAK-1), and TNF receptor-associated factor 6 (TRAF6). Furthermore, we demonstrate that the enforced expression of miR-146b in human monocytes led to a significant reduction in the LPS-dependent production of several proinflammatory cytokines and chemokines, including IL-6, TNF-α, IL-8, CCL3, CCL2, CCL7, and CXCL10. Our results thus identify miR-146b as an IL-10-responsive miR with an anti-inflammatory activity based on multiple targeting of components of the TLR4 pathway in monocytes and candidate miR-146b as a molecular effector of the IL-10 anti-inflammatory activity.
authors.affiliation: Department of Medical Biotechnologies and Translational Medicine, University of Milan, 20089 Rozzano, Italy.
authors.forename: Graziella
authors.initials: G
authors.lastname: Curtale
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Mirolo
authors.forename: Tiziana Ada
authors.initials: TA
authors.lastname: Renzi
authors.forename: Marzia
authors.initials: M
authors.lastname: Rossato
authors.forename: Flavia
authors.initials: F
authors.lastname: Bazzoni
authors.forename: Massimo
authors.initials: M
authors.lastname: Locati
mesh_terms: D002478:Cells, Cultured; D016207:Cytokines / Q000096:biosynthesis; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D016753:Interleukin-10 / Q000502:physiology*; D035683:MicroRNAs / Q000502:physiology*; D009000:Monocytes / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
chemical_list: D016207:Cytokines; D018836:Inflammation Mediators; C542542:MIRN146 microRNA, human; D035683:MicroRNAs; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D016753:Interleukin-10